Currently the gear shifting of a power gear-shifting transmission uses a gear oil in the chamber of the transmission as a control oil to achieve gear shifting, and this power gear-shifting manner has following problems:
1. the gear oil can be easily mixed with air due to high speed rotation of the gear in a gear box and then has bubble, and the gear oil having many bubbles, which is used as a control oil to conduct gear shifting, will render the gear shifting pressure of the gear box unstable and then easily burn out a clutch friction disc;
2. the cleanliness of the oil in the transmission has great influence on the gear shifting pressure; as the oil in the transmission in the prior art is oil subjected to high speed rotation of the gear, it has minute impurities, which renders insufficient gear shifting pressure and then affects the gear shifting;
3. the oil level of a gear oil usually bumps with the whole machine, which easily renders air suction of a gear shifting pump, and then also renders unstable gear shifting pressure, and if the oil level of the gear oil is increased, a churning loss will be huge; and
4. for an engineering machinery such as a grader, it also has the problem that the gear shifting pump easily sucks air during uphill and downhill, and the gear shifting pump has the hidden trouble of sucking air.